Motor-control system



A. E. BOGGS AND A. HECKMAN.

MOTOR CONTROL SYSTEM.

APPLICATION FILED MAY 6.1915.

Patented June 14, 1921.

// Haisf l3 INVENTORS Add/son E. Boqqs 5r WITESSES Auqusf H90 kman.

:ATTGRNEY UNl'I'ED STATES PATENT OFFICE.

ADDISQN BUGGS, @F PITTSBURGH, AND AUGUST HECKMAN, F WILKINSBURG, PENNSYLVANIA, A$$IGNUR$ TO WE$TENGHOUSE ELECTRIC AND, MAN'UIEAfi TURIXTG GGMYAIilY, A CQRPORATION OF YEN'NS'YLVANIA.

MOTflR-fiONTROL SYSTEM.

Specification of- Letters Patent.

Patented June 14, 1921.;

tems and particularly to such systems as are employed in connection with cranes, hoists and similar machines.

Our invention has for its object to provide a simple and efiicient means whereby a motor circuit may be completed for operation in the reverse direction after it has been opened by a limit switch.

In the operation of a crane or hoist which embodies a winding drum and a cable having a block connected to its free end, it may -occur that the block will be drawn into en ageinent with the winding drum and therey cause considerable damage. It has been proposed, heretofore, to provide a limit switch which is actuated by .a moving part, connected either to the windin drum or the crane block, to open a switch in the motor circuit when the crank block has reached a predetermined point in its path of movement toward the drum. It is necessary, however, to provide some means whereby the crane block may again be lowered after the circuit has been opened by the limit switch. It is desirable, also, to in sure that the motor cannot be operated to draw the crane block towardthc drum after the motor circuit has been completed by the auxiliary means. According to the present invention, the motor circuit is controlled by an electromagnetic switch having an actuating coil that is in circuit with a limit switch. The latter is opened when the crane block is within a predetermined distance of the winding drum. A controller for the motor is provided with an additional pair of contact members which close the circuit of the actuating coil of the electromagnetic switch when the controller is operated to reverse the motor. By means of this arrangement, it is possible to operate the motor for lower- .control resistors .11.

ing thecrane block at any time after the motor c1rcuit has been opened by the limit switch and to prevent the operator, by inadvertence or mistake, from closing the motor circuit for operation to raise the crane block. n

D In the accompanying drawing,-Figure 1 1s a diagrammatic View of circuits and apparatus embodying our invention. Fig. 2 is a diagrammatic view of an electric crane constructed in accordance with our invention. Fig. 3 is a View, similar to Fig. 1, of

a modification.

Referring particularly to Fig. 1, an electric generator 1 supplies current to an electric' motor 2 having a series field winding 3. The motor 2 may be operatively connected to any suitable mechanism as, for example, a Winding drum 4 (Fig. 2). The motor circuit is controlled by an electromagnetic switch 5 having an actuating coil 6 that is in circuit with a master switch or limit switch 7. The motor is controlled by a controller 8, of the drum type, having bridging contact arms 9 which coact with relatively movable contact members 10 to The. controller 8 is provided, also, with a contact member 12 which is grounded to the controller structure in any suitable manner and which coacts with a contact member 13 that is in circuit with the actuating coil 6.

The mechanism for opening the limit switch 7 is illustrated in Fig. 2. The motor .2 is operatively connected to the winding drum i from which is suspended a cable 15 and a block 16. A. bar 17, which projects into the path of movement of the crane block 16, is connected to the movable member of the switch 7 by a link 18. It will be obvious that, when the block 16 reaches a predetermined point in its upward movement, the switch 7 will be opened to break the motor circuit.

It may be assumed that it is desired to hoist a load by means of the cable 15 and the block 16. It may be assumed, further, that the limit switch 7 is closed to complete the circuit of the actuating coil 6 which is energized to close the main switch 5. The controller 8 will be actuated to the left to complete the motor circuit for operation in such direction as to hoist the load.

When the block 16 reaches a predetermined pointthrough the other controller.

in its path of movement, the bar 17 will be actuated to open the limit switch 7 to deenergize the actuating coil 601 the switch 5. The latter then opens to break the motor circuit, and the block 16 comes to rest in such position that the limit switch cannot be closed until the block has been lowered.

The controller is then actuated to the right to the lower position to effect engagement of the contact members 12 and 13. The circuit of the actuating coil 6 is again completed and the motor circuit is closed. The block 16 may then be lowered to such point that the limit switch 7' may be closed and the bar 17 placed in position for operation as a safety device in case the block 16 again approaches the drum 4.

A modification of our invention is illustrated in Fig. 3, in which similar numerals are employed to indicate corresponding parts. In this form of our invention, a main motor 2 and an auxiliary motor 19 are employed to operate windin drums similar to that shown in Fig. 2. The supply circuits of the motors 2 and 19 are controlledby an electromagnetic switch 5 havin an actuating coil 6 that is in circuit with imit switches 7 and 20. The limit switches 7 and 20 are adapted to be actuated by crane blocks 16 that are respectively connected to the motors 2 and 19. a

The motors 2 and 19 are respectively controlled by controllers 8 and 21. Each of the controllers 8 and 21 is provided with a grounded contact member 12 and a coacting contact member 13 similar to that described in connection with the controller 8 of Fig. l. The'controllers8 and 21 are electrically interlocked in such manner that one of them must be in the off position in order that the circuit of the magnet coil of the main switch5 may be completed Thls' arrangement is desirable in orderto prevent the crane block of one hoist being drawn into its corresponding drum while the main circuit is completed through the electromagnetic switch b the other hoist controller. Each of t e controllers 8 and 21 is provided with a pair of contact members 22 in circuit with the actuating coil 6 and bridged by a contact member 23 only when the controller is in its off position.

It may be assumed that the limit switches 7 and 20 are closed and that the controllers 8 and 21 are in their off, or inoperative, positions. The circuit of the actuating coil (3 then extends from a positive line conductor 24, through the coil 6 and limit switches 7 and 20 to ground and thence to a negative line conductor 25 which is grounded. The coil 6 is energized by the circuit just described to close the switch 5.'

It may be assumed that the controller 8 has been actuated to lts hoist position,

and that the main motor has actuated its crane block to such position that the correspondin limit switch 7 has been opened to break 1318 circuit of the coil 6. The supply circuits. for both motors are then opened. It is desirable, however, that the main motor 2 may be operated in the reverse direction to lower its load. It is possible, also, that the auxiliary controller may have been in an operative position when the supply circuit was broken at the switch 5. It is essential, therefore, that the closing of the supply circuit, upon the reversal of themain motor 2, will not cause the operation of the auxiliary motor, as its'limit switch is not then effective to break the supply circuit.

The actuation of the main controller 8 to its lower position to efi'ect the engagement of the contact members 12 and 13 completes a circuit (assuming that the auxiliary controller is in its off position) which extends from the positive conductor 24 through coil 6, contact members 22 and bridging contact member 23 of the controller 21, contact members 12 and 13 of controller 8 to ground, and thence to the negative line conductor 25 which is grounded. The main motor 2 may then operate to lower the load, but the auxiliary motor 19 cannot be operated because the actuation of its controller from its off position opens the circuit of the actuating coil 6, and the supply circuit is broken. In the same manner, the operation of the main motor 2 is prevented if the limit switch 20 is opened, and the circuit of the coil 6 is completed b reversing the controller 21. The circu1t of the coil 6 can be completed by the controller 21 only when the controller 8 is in its off position.

While we have shown and described a ground return for the circuit established by the auxiliary contact members for shunting the limit switch, it will be understood that a metallic circuit may be substituted therefor without departing from the spirit of our invention.

It will be noted that We provide a simple and eflicient arrangement for reversing an electric motor after its further movement in one direction has been prevented by the opening of a limit switch. We provide, also, means for insuring that one of a pair of motors, the circuits of which are controlled by the same switch, cannot be operated when the circuit of the other motor motor, and means for preventing the opera-' tion of said corresponding motor when the other,controller'is also operated.

3. In a motor-control system, the combination with a pair of electric circuits each including an electric motor, and a controller for each of said motors, of means for closing the circuit of one motor when the other motors controller is moved to an inoperative position and for breaking said circuit of said onemotor when said other motors controller ismoved to an operative position.

4. In a motor-control system,the combination with a pair of electric motors, and a controller for each of said motors, of means for operating one'of said motors when the other motors controller is in inoperative position, and means for preventing the op-, eration of either motor when the said controller is moved to operative position during the operation of said first motor.

5. In a motor-control system, thecombination with a pair of electric motors and a controller for each of said motors, of means for rendering said controllers inefi ective, and means carried by each controller for I rendering the other controller effective.

6. In a motor-control system, the combination with a pair of electric motors and a controller for each motor, of means'carried by each controller for controlling the effect of the 0 eration of the other controller, and means or rendering said othercontroller inflective when said first means is in an.

inoperative position.

7. In a motor-control system, the combination with a air of electric motors and a normally close switch for each of said motors, of means for automatically opening the switches at predetermined points in the operation of said motors, means for opera-tip either motor when both switches are close and means for preventin the operation of either motor when the ot er motors switch is open.

8. In nation with a plurality of electric motors and a normall closed switch for each momeans for prea motor-control system, the combiventing the operation of one motor when another motor s-switch. is open.

9. In a motor-control system, the combination with a pair ofelectric motors and a controller and a limit switch for each mo tor, of means for automatically opening the limit switches at predetermined points in the o eration of said motors, and means where y either controller may operate to reverse its motor, when the corresponding limit switch ,is open, only whenthe other controller is in an inoperative position.

10. The combination with a pair of electric motors, of a switch for closing the cir cuits of said motorshaving' an actuating coil, and a pair of limit switches for together closing the circuit of said coil and respectively adapted to be opened upon said motors occupying predetermined positions.

11. The combination with 'a pair of electric motors, of a pair of limit switches for together effecting the closing of the circuits of said motors and-respectively adapted to be opened upon said motors occupying predetermined positions, means for preventing the operation of one of said motors upon the opening of the other motors limit switch, and means for preventing the further operation of said other motor except in the opposite direction.

. 12. The combination with a pair of election.

13. The combination with a pair of motors, a freely movable controller for each of said motors, and a switch for closing the circuit of each of said motorsand adapted .to be opened at a predetermined point in the operation of the corresponding" motor,

of means carried b l said controllers forclosing thecircuits 0 said motors independently of said circuit-closin switches, andelectrical means for connecting s'aid controllers,.r whereby the actuationof each of said controllers toan operative-position when its corresponding circuit-closing switch is open is ine ective to complete the circuit of the corresponding motor when the other controller is in an operative position.

In testimony whereof, we have hereunto subscribed our names-this 29th day of April, 1915.

l ADDISON E. BOGG S. E AUGUST'HEOKMAN. 

